1. Field of the Invention
The invention relates to the field of ultrasonic scanning for medical applications, particularly devices for providing both B-scan and Doppler data.
2. Prior Art
Numerous ultrasound scanners are commercially available for diagnostic procedures. In one class of these scanners, a B-scan display is presented to the operator. The operator selects a point with a cursor in this B-scan display. An ultrasound beam is directed to the point and the echoes processed to obtain the Doppler shift. The major application for these systems is to evaluate the effects of arteriosclerosis in the peripheral vascular system, primarily carotid, femoral and popliteal arteries. Possible areas containing plaque within the lumen of vessels can generally be identified in the B-scan display, and then with use of the Doppler signal, the "rushing" sound of the blood through these obstructed areas is vividly heard. Severe obstructions cause larger accelerations along with turbulent flow. This turbulent flow includes reverse flow which is also monitored.
In one prior art system, a pluraltiy of transducers are mounted about a common axis with their beams extending radially from the axis. As the transducers are rotated past an ultrasound window which is in contact with the body, data for a B-scan display is obtained. When the operator finds an area within the B-scan requiring a Doppler examination, the rotation of the transducers is stopped. Then a single transducer is aimed at the area of interest and the echoes from this transducer processed to sense the Doppler shift. There are several problems with this prior art device. First, during the time of the Doppler examination, the operator is not certain of the precise point from which the Doppler returns are received. The reason for this is that the B-scan data is not simultaneous with the Doppler data (i.e., the rotation of the transducers is stopped during the Doppler mode). Also since the same transducers are used both for the B-scan and Doppler data, the frequency of the transducers cannot be optimized for each mode. Another problem encountered with this prior art device is that when a transducer is in a normal position relative to the body there is no Doppler shift if the Doppler beam is perpendicular to the blood flow direction.
As will be seen, the present invention provides both simultaneous B-scan and Doppler data with separate transducers. The Doppler transducer of the present invention is off to the side of the B-scan transducer, therefore assuring a better Doppler return.
In another prior art imaging system, the above-mentioned rotating transducers are used for a B-scan display and a separate transducer for Doppler data. With the configuration of this device, precise alignment of the Doppler beam within the field of view of the B-scan beam is not assured because of the mounting employed. Morevoer, simultaneous operation as in the present invention is not provided.
In still another prior art system, a single, split transducer is employed. (That is, each transducer half is of a semicircular shape). Each of the transducer halves moves independently, one providing a B-scan display and the other, Doppler data. With this system, there is limited flexibility in positioning the transducers to provide both B-scan and Doppler data. Also, this system has a long fluid path between the transducer and the patient, and is thus not hand-holdable.